High density radiation (HDR) brachytherapy procedures depend upon delivering fractionated therapy doses to designated target volumes by timed insertion of a small (2-4 mm long) seed radiation source of, for example, Ir-192 into body cavities or tumors. The Ir-192 source is attached to a wire and pushed/pulled through previously surgically inserted catheters. Presently, HDR procedures rely on computer controlled mechanical delivery systems to track the location of the source in the body. While such a source tracking method is generally acceptable, in some case there has been movement of the surgically inserted catheter between the time of insertion and the time of brachytherapy treatment resulting in mislocation of the seed source. In extreme cases, the seed source can become “lost” in the body. In such cases, exposure of the patient to such high radiation doses for an extended period of time during the search for the seed source and removal thereof can result in the death of the patient. Thus, a device and method for the real time, in situ tracking of seed sources would be highly desirable to assure the proper location of the seed source during treatment and location of the seed source in those rare instances where it becomes lost in a body cavity or tumor during or after treatment.
Such a method and device were described in a paper entitled, “Feasibility Study of in situ Imaging of Ir-192 Source During HDR Brachytherapy Procedure Using Small Gamma Imager Based on a Hamamatsu R3292 PSPMT” presented at the IEEE Nuclear Science Symposium at Seattle, Wash. on Oct. 29-30, 1999 and subsequently published on CD in the year 2000. This paper is incorporated herein in its entirety. The apparatus described in this paper comprised a dedicated compact gamma camera based on a 5″ Hamamatsu R3292 position sensitive photomultiplier and a thin Bicron BC 400 plastic scintillator. The low efficiency plastic scintillator detector provided acceptable images of a 5.3 Ci Ir-192 source when viewed through a single pin hole collimator (hole diameters 0.5 and 1.0 mm) located 16 cm from the source. While this gamma camera provided a solution to the problem of verifying HDR brachytherapy treatments, it did not provide in vivo locational information such as the exact depth of the seed source in the body. In other terms, it provided a two dimensional location on the surface of the body, but the depth of the seed within the body was not determined, thus, providing the possibility for some error in the exact location of the seed in the body cavity or tumor, and in the case of “lost” seeds, the ability to accurately locate the seed for removal.
Thus, a method and device that are capable of providing accurate, three-dimensional locational information regarding the seed source in a body cavity or tumor would be highly desirable.